In 1983 the Infrared Astronomical Satellite (IRAS) discovered that starburst galaxies represent about 30% of the total energy budget in the Universe today.  Since most of the power output, or luminosity, of starburst galaxies is due to young stars still within their dusty birthplaces, starburst galaxies must represent more than 30% of all the stars forming in the Universe today.  In fact, if more than 1/3 of the energy budget of our Universe is due to visible starlight from medium and old age stars, then starburst galaxies represent the main source of new stars in our universe!

Most galaxies contain a large population of old stars.  Often this old population is segregated from the younger stars.  Most of the old stars usually appear in an elliptical bulge surrounding the center of the galaxy.  The young stars are usually formed within the disk.  These old populations do not look like they have had any young stars in them for about 10 billion years. 

Since the age of the Universe is probably 10-14 billion years, this does not leave much time for these galaxies to have formed.   These bulge populations are probably the result of starbursts that occurred when the Universe was much younger.

Astronomers have also discovered strong evidence that quasars (the most luminous objects in the Universe) are just the final growth stages of super-massive black holes that are born within starbursts.  Black holes form when massive stars explode, or "supernova". 

Many astronomers think that the super-massive black holes seen in quasars got their start from very luminous stars that formed in whopper-scale starbursts, a hundred times the power output of our Milky Way.  Such ultraluminous starburst galaxies can be seen from enormous distances, even with small infrared telescopes.  Since it has taken billions of years for their light to reach us from their great distances, they will help us to trace the history of star formation in our Universe and may trace the formation of quasars as well.

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Last Updated: 12/2/98